Feature Article

Public-Private Partnership on In-Situ Measurements in the Gulf of Guinea

By Dr. Rémi Estival ' Valérie Quiniou ' Christophe Messager

A map of the number of sea surface temperature observations from the MODIS satellite in 2011.

In-situ measurements are crucial for remote-sensing observations, and hindcast and forecast modeling. Hence, in-situ data are often used to calibrate and correct satellite data, or they are merged and processed with other in-situ data and remote-sensing observations to improve the quality and coverage of environmental monitoring. These data are also used to improve global Earth modeling. For instance, the National Centers for Environmental Prediction and the National Center for Atmospheric Research (NCEP/NCAR) Reanalysis 1 project incorporates observations and model outputs to provide a gridded data set of atmosphere parameters over large regions.

For modeling, in-situ data are used to analyze or validate ocean and meteorological model outputs. They can also be assimilated to correct the model locally (as for the NCEP/NCAR reanalysis) and serve as initial and boundary conditions. Therefore, the reliability of the simulations or reanalysis products often depends on the quality and amount of data in the monitored area. However, access to these data as soon as they are collected is a real issue when it comes to forecast quality.

Lack of In-Situ Measurements
In the Gulf of Guinea
The Gulf of Guinea is located in the equatorial East Atlantic Ocean, between Cape Lopez in Gabon and Cape Palmas in Liberia. In this instance, it is considered also to include Congo and northern Angola. This tropical region benefits from a high level of incoming solar radiation with an important meridional gradient of temperature, enhanced between the ocean and the continent. These irregular surface energy distributions induce regional and subregional low-level atmospheric circulations.

Moreover, the ocean gains heat from solar flux, which is released mainly through latent heat (evaporation) fluxes to the atmosphere. This contributes to high cloud coverage in the area, which is the major limiting factor to the use of remote sensing. In 2011, between Guinea and Angola, around 90 percent of NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) data were obscured by clouds. The MODIS satellite has provided on average less than one observation every two weeks in 2011 because the area has cloud cover most of the time.

Additionally, intense precipitation and strong freshwater discharges from the Congo and Niger rivers modify the velocity field in the ocean and tend to flush drifting buoys offshore away from the river plume. Hence, very few drifters can be seen along the coast between Nigeria and Congo.

Consequently, NASA's Autonomous Temperature Line Acquisition System (ATLAS) buoys from the Pilot Research Moored Array in the Tropical Atlantic (PIRATA) programs provide the main sustainable observations in the Gulf of Guinea. Four buoys have been installed in the equatorial East Atlantic Ocean, and a weather station has been placed in Sao Tomé. Thus, over a typical year, few observations are available in the coastal region of Western Africa.

In-Situ Measurements on Oil and Gas Platforms
The Gulf of Guinea and, more generally, Western Africa have many oil and gas resources, and major industry players are present in the region. When in production, platforms are surrounded by vessels or helicopters that require ocean and weather monitoring to secure operations. For safety, most of the platforms with a helideck have an operational weather station; those equipped with an oil offloading system to tankers often have instruments to measure sea state and near-surface currents.

However, most of the time, these monitoring systems have no remote connection, and data are not available in real time or, in the best case, only available within the company network. Remote access to real-time data would improve the safety and the organization of marine and air logistics operations, provide valuable modeling information and help predict drift in case of oil spills. It would also secure data by simplifying archiving and sensor maintenance. The archived data could then be used to improve design criteria for new platforms in the area.

Most of the oil and gas resources are localized on the continental shelf, which has been divided into blocks where companies conduct exploration and production. Measurements in those areas would complement existing ocean and weather observations. Introducing these data in a global system, such as the World Meteorological Organization's (WMO) Global Telecommunication System (GTS), and providing free access to the scientific community would improve weather and ocean forecasts to the benefit of civilians as well as the oil and gas industry. To continue this article please click here.

Dr. Rémi Estival has a Ph.D. in submarine acoustics and a master's degree in mechanics. He was employed by Total to set up a real-time network of ocean and weather stations. His work is hosted by ICEMASA (International Centre for Education, Marine and Atmospheric Sciences over Africa) and University of Cape Town.

Valérie Quiniou is the head of Total's survey technologies department for geophysics, geotechnics, metocean and geomatics applied to development and operations. She joined Total in 2002 as a metocean advisor, after working with Noble Denton and Bouygues Offshore (now Saipem). She graduated as an engineer from École Polytechnique and ENSTA (École nationale supérieure de Techniques Avancées).

Christophe Messager founded ICEMASA (International Centre for Education Marine and Atmospheric Sciences over Africa) in 2008 and led it until 2011. He is one of the promoters of the Guinea Gulf data collection project. He presently researches ocean-atmosphere interaction and is involved in international climate and meteorological modeling programs, as well as in-situ data collections.

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